Crystal working apparatus



A. 10, 1943. s, 'a y 2,326,319

, CRYSTAL WORKING APPARATUS Filed March'lB, 1942 2 Sheets-Sheet 1 Aug.10,1943. R, s, BNLEY 2,326,319

CRYSTAL WORKING AFPARATUS Filed March 12, 1942 2 Sheets-Sheet 2 Patented Aug. 10, 1943 CRYSTAL WORKING APPARATUS Richard S. Bailey, Baltimore, Md., assignor to Bendix Aviation Corporation, South Bend, Ind., a corporation of Delaware Application March 12, 1942, Serial No. 434,389

15 Claims.

This invention relates to the cutting of crystalline materials, and more par icularly to the cutting of plates from a mother crystal in which the plane of the. plates is oriented in accurately predetermined relationship to the crystal axes, as in the manufacture of piezo-electric quartz resonators wherein the operating characteristics of the resonator are controlled by variations in this orientation.

Piezo-electric resonators, or crystals as they are usually termed, are-widely employed in the radio industry for the precise control of oscillatorfrequencies. These crystals are most often in the form of slabs, bars or plates which have been cut out of a mother crystal of quartz. For

many years the crystal plates were cut out parallel to the optical or Z axis and perpendicular to either the X (electrical) axis or the Y (mechanical) axis, and it was found that they controlled the frequency of an oscillator very rigidly except sion of the information pertaining to the location of the crystal axes within the rough bar from temperature coefficient could be reduced substantially to zero, 1. e. less than two parts per million per degree centigrade. The attainment of a temperature coefficient of this order requires the 'most precise determination and maintenance of the angle of the cut in production. In the manufacture of the crystals first described above having a high temperature coefficient, exact control of the cutting angle was not vitally essential, for

the finished product was employed in a constant temperature oven and variations in the temperature coefiicient were thus rendered innocuous.

- the cutting angle, but one which does not meet the exacting control requirements in the manufacture of the modern crystal element. Two prolific sources of difliculty in the old system are:

the error in marking the rough bar to indicate the axes, and the error in aligning these markings with the indices on the cutting machine. These errors are seen to arise because of the need for intermediate indical markings for the transmisthe apparatus for locating those axes to the cutting machine using those axesas a reference. The variations in temperature coefilcient occurring when the above coarse control of the cutting plane is employed, are so great that its use in the manufacture of high grade low temperature coefiicient crystals has perforce been abandoned.

In the first manufacture of the later described crystals, the rough bar of stock was mounted in the chuck, a sample plate of the crystal cut off, and this'sample was then put through all the subsequent processing afterwhich its temperature coefiiclent was measured. If the coefficient was satisfactory, the rest of the bar was cut at the same angle or setting of the machine, but if the drift was excessive a new angle of cut was empirically selected and the above steps repeated until a satisfactory sample plate had been cut. Thereafter the remaining stock was .cut at the same angle as that giving the satisfactory sample. Every time cutting operations were begun on a new bar of crystal stock it was necessary to repeat the above procedure, which obviously is wasteful of time, money, and material. Up'to the prese t time, however, the small manufacturer of crystals has been forced to cling to these ineflicient methods because of the expense of X-ray apparatus for determining the crystal axis orientation, which method is described in the following paragraph.

The regular orientation of molecules within the crystal structure confers the properties of the well known diffraction grating on crystalline materials for wavelengths comparable to the molecular spacing. 'The wavelengths required fall within that portion of the radiation spectrum which we define as X-rays.- The deviation produced by a diffraction grating depends on the wavelength of the incident energy, the spacing of the grating elements, and the angle existing between the grating plane and the energy beam. When working with a given substance, such as piezo-electric quartz, the spacing of the grating elements, 1. e. molecules, is constant, and a monochromatic beam of X-rays is obtained by the use of selected targets in conjunction with appropriate filters. With these elements constant, the crystal axes may be located by observation of the angular deviations of the diffracted beam. In operation, a plate is cut from the crystal bar, and

\ this plate is mounted in suitable X-ray diffraction measuring equipment whereby the orientation of a face or faces of the plate with respect to the 'crystal axes is determined." From this data a correction angle is determined, should the plane of the cut not already be in the desired position, and the work holder or cutting tool may then be readjusted by an amount equal to the correction One of the principal objects of this invention is to provide improved apparatus for accurately detenining the angle between a cutting plane and the axes of the crystal stock undergoing the cutting operation, which is precise, occupies a minimum of space, and of relatively nominal cost.

Another object of this invention is to provide novel apparatus for precisely determining the angle between a cutting plane and the axes of crystal stock undergoing the cutting operation,

which does not require the cutting of sample plates from the stock.

A further object of the invention is to provide novel apparatus for precisely determining the angle between a cutting plane and the axes of a crystal bar undergoing the cutting operation without removing the crystal bar from the work holder.

Still another object of the invention is to provide novel apparatus for precisely adjusting the angle between a cutting plane and the axes of a crystal bar undergoing the cutting operation in which the orientation is made without the necessity of referring to intermediate scribed lines on the bar and indicial markings on the cuti mg machine.

The above objects and advantages of the invention are accomplished by providing means for moving the work holder about an axis fixed with respect to the cutting plane so that the bar being cut is transferred by rotation about said axis from the working position to a position suitable for the determination of a crystal axis by the use of a stauroscope which is fixed with respect to the frame of the cutting machine, all this without removing the bar of stock from the workholder. In brief, the bar is restricted to one degree of freedom, and is -moved back and forth in this degree of freedom between the working position and the means for determining crystal orientation, as required.

Other objects and advantages will in part be disclosed and in part be obvious when the following specification is read in conjunction with the drawings in which:

Figure 1 is a view in perspective of the complete cutting machine.

Figure 2 is a top view of the work holder.

Figure 3 is a view in perspective of the crystal bar mounted in the bar holder.

It is to be understood that these drawings are intended to illustrate one of the many forms in which the invention may be utilized and are not to comprise a, limitation in. the content or scope of the invention.

In the drawings, like parts are designated by like reference characters.

, The holder arm I may thus be rotated about the axis defined by the two bearings II. The fixed scale I2 is secured immovably to the outer end of the arm I0, while the movable scale M is rigidly fixed to the slide I3 which is adjustably secured to the outer end of the arm ID by the clamping bar screw I5. The'bar of piezo-electric quartz I6 is cemented into the bar holder H which is secured in the bar clamp I8 by set screws (not shown). The bar clamp I8 is attached to a carrier not shown in the drawingswhichis longitudinally adjustable along the track in the slide I3, thereby providing a means of advancing'the around the axis defined by the bar screw and to the saw 3 may be regulated by adjusting the Referring to Figure 1, the base I carries the position of the counterweight l9 along the counterweight arm 20, this arm being secured to the holder arm III as shown. At the completion of the cut, the bar I6 is prevented from falling against the housing 8 by the stop 29 located under the arm I0 and limiting its angular travel in the downward direction to the desired amount.

During the cutting operation, the work is prevented from chattering, with consequent chipping of the crystal blank, by the dash pot 34, which is connected to the holder arm III by the rod 35 in the'manner shown, a wing nut 36 serv ing to attach or detach the .rod 35. 4

Also mounted on the base I, is the stauroscope comprising the light source 2|, the polarizer indicated generally at 22, and the analyzer indicated generally at. 23 with an eyepiece 30, the analyzer carrying, in addition to the polarizing element, a'Calderon double plate of calcite, such as is well known in the art of crystallography for increasing the sensitivity of extinction angle indications under polarized light. The polarizer 22 is adjustable along the length of the tubular standard 2Lsecured to the adjustably rotatable scale plate 25.

The entire stauroscope assembly may be rotated by rotating the scale plate 25 about an axis preferably passing through the line of sight of the stauroscope elements, and the angular position may be read on the scale of plate 25 in cooperation with the vernier scale 26 adjacent thereto. The thumbscrew 32 afiords means for locking the assembly in any desired angular position. As the exact details of stauroscope construction are recited in many crystallographic texts, and are generally known in the art, it is not felt necessary to repeat the recitation here. The bar clamp I8 on the holder arm I0 with its associated elements may be rotated about the axis defined by the bearings I l to the alternative position shown in dotted lines, after disconnecting the dashpotj34 by removing the wing nut 36, placing the crystal bar I6 at the working stage of the stauroscope, this stage being indicated generally at 3 I. The arm I 0 is maintained in this position by the stop 21 attached to the upright 9.

Turning to Figure 2, the-holder arm III, with the associated elements, is shown more clearly as it appears when midway in the transfer between the cutting position and the stauroscope working stage. This view also shows the crank 28 which drives a threaded rod rotatably secured to the slide I3 and passing through a threaded asaasie a a 3 opening in the carrier for the bar clamp ll. Rotation of the crank 28 thus advances the carrier alongthe track in the slide it, carrying the bar clamp IS with it. The thickness of the blank which is cut oil! from the crystal bar it is regulated by the amount of advance given by the rotation of the crank. I

Theview ofFlgur-e3 showsthe crystalbar I! mounted in'the bar holder l'l, plaster of Paris II being commonly used for the mounting operation. The bar is cut out of the mother'crystal with the axes located as nearly in the position shown as possible.

In operation, the stauroscope is first adjusted. The-polarizer and analyzer are crossed to provide minimum transmission of light from the source 2| to the eyepiece 30 and the Calderon double plate is then adjusted until both halves appear to be the same grey color. Briefly, the Calderon double plate consists of a plate made up of two pieces of calcite rotating the plane of polarization of a beam of polarized lightin opposite directions and joined along a common bisectin'g line. For this reason both halves cannot appear dark simultaneously under the crossed polarizer and analyzer, and the balance of the intensity with which the two plates appear is an extremely sensitive indicator of any change in the plane of polarization of, the light passmg from the polarizer to the analyzer. The appearance of the Calderon double plate is unchanged only when the Z and Y axes lie parallel to the two rectangular vibration directions of the polarizer and analyzer.

Therefore the intensities of the two halves of the Calderon plate appear balanced at four points as the crystal is rotated 360 degrees about an axis parallel to the X axis under the stauroscope.

During the preparation of the bar l6, all necessary cuts are made in such relation to the axes of the mother crystal that the approximate location of each of theaxes within the bar is known. The bar is tested in convergent polarized light to determine whether the crystalline structure is right handed or left handed, marked accordingly, and a test is then made to determine the polarity generated along the X axis under impact, the faces normal to the X axis being marked in accordance with the results of this test. Inthe manufacture of one type of low temperature coefiicient crystal, namely that known as the AT cut, it is required that the plane of the cut lie at plus 35 degrees to the Z axis in right handed. crystals, or at minus 35 degrees to the Z axis in left handed crystals. In each case, 5

however, the major plane surfaces of the plate are parallel to the X axis. Since it is not convenient to provide this range of adjustment in the cutting machine, the expedient adopted as a solution is to insert right handed crystal bars into the holder with the positive face up, or left handed crystal bars with'the negative face up.

In the initial set up of' the apparatus, the bar l6 and bar holder I! are fastened in the bar clamp l8, and the bar so orientated that its optical axis (the Z axis) makes an angle of approximately 35 degrees with the saw blade 3. A test out is now taken and the resulting .crystal plate passed through the normal finishing processes and its temperature coemcient measured. 7

Should the coefflcient be other than the desired value, the bar screw I5 is loosened and the work holder rotated through a small angle which is conveniently read on the scales i2 and I4, there- 'is then orientated for'balanced illumination of the Calderon plate. The reading on the scale 2| may now be recorded for future reference in the manufacture of crystals of this particular type and the stauroscope locked in this position using the thumbscrew 32. The arm i0 is now returned to the cutting position and the remainder of the bar it cut into plates or slabs in the usual-manner. Upon the insertion of a new bar into the work holder, the arm I. is placed in the position for stauroscopic observation, after the bar has been coated with oil, thebar screw l6 loosened and the work holder is rotated about the axis passing through the bar screw until the Calde-on plate shows balanced illumination. The bar" screw is now tightened, thus securing the crystal bar in the desired position, and the arm I0 is returned to the cutting position. Because of the control imposed in the original preparation of the bar from the mother crystal with respect to the approximate orientation of the axes in the .bar, it is 'a simple matter for the operator to in- 7 sure that he works only to the desired orientationof the axes among the four null or balance 7 positions which may be obtained, by simple visual observation of the physical orientation of the bar. As an additional safeguard, the range of adjustment may be limited to less than 90. degrees but still made larger thanthe anticipated variation in the position of the Z axis within the bar.

The manufacture of BT and CT cut crystals is accomplished with equal ease once the initial reference position of the stauroscope has been'determined. In setting up for subsequent production runs, thestauroscope scale 25 is set to the predetermined reference position for the particular cut of crystal being manufactured, and all bars are orientated for balanced illumination of the Calderon plate in the manner above outlined, after which successive cuts of the desired thickness are taken from the bar. The saving in time and material over the first described. out and try method is obvious, and the adjustment of position is made directly in the machine without the intermediate steps and the expensive equipment required in using X-rays for this purpose. In the apparatus disclosed, only a'few seconds of time are required for adjusting the bar to within 5 or 10 minutes of the desired cutting angle.

While I have shown the work holder rotatably movable with respect to the stauroscope, it is obvious that the stauroscope may be made the movable element or that the separating motion may be one of translation rather than one of rotation. The results which I have achieved have been accomplished by making'the stauroscope and workholder relatively movable with a single,

after retightening the bar screw l5 and taking 75 departing from the spirit thereof as expressed in the foregoing description and in the appended claims.

I claim:

1. In apparatus for the cutting of crystalline materials, a base, cutting means attached to said base, a work holder mounted on said base, and means utilizing radiant energy for locating predetermined molecular planes within a crystal located in said work holder mounted on said base, said work holder and said locating means being relatively movable with asingle degree of freedom.

2. In apparatus for the cutting of anisotropic crystalline substances, a base, cutting means attached'to said base, a work holder, and means utilizing light energy mounted on said base for the location of predetermined molecular planes within said substances, said work holder and said optical means being relatively movable with a single degree of freedom.

3. In apparatus for the cutting of anisotropic crystalline substances, a base, cutting means attached to said base, a work holder, and means utilizing light energy mounted on said base for the location of predetermined molecular planes within said substances, said work holder and said optical means being relatively movable between predetermined positions with a single degree of freedom.

4. In apparatus for the cutting of anisotropic crystalline substances, a base, cutting means attached to said base, a work holder, optical means for the location of crystalline axes within said substances mounted on said base, means for adiustably rotating said optical means about an crystalline substances, the combination of rotatable cutting means, optical means for the location of crystalline axes within said substances,

and a work holder movable between said cutting means and the observation stag of said optical means about an axis of rotation parallel to the axis oi rotation of said cutting means, said work holder also being adjustably rotatable about an axis substantially perpendicular to said axis of rotation.

9. In apparatus for the cutting ofanisotropic crystalline substances, 9. base, cutting means attached to said base, a work holder, and stauroscopic means mounted on said base, said work axis passing through the line of sight, and means for moving said work holder and said optical means relatively within a single degree of freedom.

5. In apparatus for the cutting of anisotropic crystalline substances, 3. base, cutting means attached to said base, a work holder, optical means 6. In apparatus for the cutting of anisotropic crystalline'substances, a base, cutting means attached to said base, a work holder, optical means for the location of crystalline axes within said substances mounted on said base, means for moving the work holder between the working stage of said optical means and said cutting means, said means permitting movement only with a single degree of 'freedom, and means for stopping the movement of said work holder at a predetermined point within the working stage of said optical means.

'7. In apparatus for the cutting of anisotropic crystalline substances, the combination of. a base, rotatable cutting means mounted on said base, optical means for the location of crystalline axes within said substances carried on said base, and a work holder movable between said cuttin means and the observation stage of said optical means about an axis of rotation parallel to the axis of rotation of said cutting means.

8. In apparatus for the cutting of anisotropic holder and said stauroscopic means being relatively movable with a single degree of freedom.

10. In apparatus for the cutting of anisotropic crystalline substances, a base, cutting means attached to said base, a work holder, stauroscopic means mounted on said base, means for adjustably rotating said stauroscopic means about an axis passing through the line of sight of said stauroscopic means, and means for moving said work holder and said stauroscopic means -relatively with a single degree of freedom.

11. In apparatus for the cutting of anisotropic crystalline substances, a base, cutting means attached to said base, a work holder, stauroscopic means mounted on said base, means for movlllg the work holder between the working stage of said stauroscopic means and said cutting means, said means permitting movement only with a single degree of freedom, and means for adjustably rotating said work holder about an axis substantially parallel to the line of sight through said stauroscopic means when located at said working stage of said stauroscope.

12. In apparatus for the cutting of anisotropic crystalline substances, as base, cutting means attached to said base, a work holder, stauroscopic means mounted on said base, means for moving the work holder between the working stage of said stauroscopic means and said cutting means, said means permitting movement only with a single degree of freedom, and means for stopping the movement of said work holder at a predetermined point within said working stage of said stauroscopic means.

- 13. In apparatus for the cutting of antisotropic crystalline substances, a base, cutting means attached to said base, a work holder, and stauroscopic means mounted on said base, said work holder and said stauroscopic means being relatively movable between predetermined positions with a single degree of freedom.

14. In apparatus for the cutting of anisotropic crystalline substances, the combination of a base, rotatable cutting means mounted on said base, stauroscopic means carried on said base, and a work holder movable between said cutting means and the observation stage of said stauroscopic means about an axis of rotation parallel to the axis of rotation-of said cutting means.

15. In apparatus for the cutting of ,anisotropic crystalline substances, the combination of rotatable cutting means, stauroscopic means, and a work holder movable between said cutting means and the observation stage of said stauroscopic means about an axis of rotation parallel to the axis of rotation of said cutting means, said work holder also being adjustably rotatable about an axis substantially perpendicular to said axis of rotation.

RICHARD -S. BAILEY. 

